1. Field of the Invention
The present invention relates to a device for hydrostatically supporting a slide. More particularly, it relates to such a device wherein a sliding movement is achieved between a first slide member having a square guide bore and a second square slide member guided by the square guide bore.
2. Description of the Prior Art
In the hydrostatic slide supporting device of this kind, a first slide member 1 is provided with a guide bore 2 having a square cross section, and a second slide member 3 having a square cross section is slidably guided by the guide bore 2, as shown in FIG. 1. In such device, a pair of hydrostatic supporting surfaces 5 are formed on each of four guide surfaces 4, which constitute the guide bore 2. The hydrostatic supporting surfaces 5 are formed at locations along the sliding direction, for example, formed at both longitudinal ends of the guide surfaces 4, as shown in FIG. 2, in order to restrict pitching movements of the second slide member 3, which is a swing movement about an axis perpendicular to the sliding direction.
Further, a pair of rectangular hydrostatic pressure pockets 6 are formed at each of the hydrostatic supporting surfaces 5 in order to restrict rolling movements of the second slide member 3, which is a swing movement about an axis parallel to the sliding direction. At each hydrostatic supporting surface 5, land portions 8 are formed to surround the hydrostatic pressure pockets 6, and a par of oil supplying nozzle 9 is disposed within each hydrostatic pressure pocket 6 in order to supply pressurized lubrication oil thereto.
When pressurized lubrication oil is supplied to the oil supplying nozzles 9, the lubrication oil flows into the hydrostatic pressure pockets 6 in order to produce a predetermined pressure in the hydrostatic pressure pockets 6, and then flows outside of the hydrostatic supporting surfaces 5 through a clearance between the land portions 8 and the outer surface of the second slide member 3.
When a pitching motion or a rolling motion of the second slide member 3 occurs, the pressures in some of the hydrostatic pressure pockets 6, which relatively approach to the outer surface of the second member 3, increase in order to return the second slide member 3 to the original posture.
In such device, the rolling motion of the second slide member 3 is restricted by the pair of hydrostatic pressure pockets 6 formed at each hydrostatic supporting surface 5, and the supporting strength changes in proportion to the square value of the distance L1 between the lateral centers of the pair of hydrostatic pressure pockets 6 along a direction perpendicular to the sliding direction.
On the other hand, the pitching movement of the second slide member 3 is restricted by each pair of hydrostatic supporting surfaces 5 formed on the guide surfaces 4, and the supporting strength changes in proportion to the square value of the distance L2 between the longitudinal centers of the hydrostatic supporting surfaces 5 along the sliding direction.
In such hydrostatically supporting device, however, the support strength against the rolling movements cannot increase so much, because the distance L1 is smaller than the half of the lateral width of the hydrostatic supporting surface 5.
Further, since the number of the oil supplying nozzles 9 increases in proportion to the increase of the hydrostatic pressure pockets 6 and the diameter of the nozzles 9 cannot be reduced so much because of machinability, the amount of the lubrication oil fed into the hydrostatic pressure pockets 6 is inevitably increased. Accordingly, the clearance between the land portions 8 and the outer surface of the second slide member 3 must be increased in order to allow the large amount of lubrication oil to flow outside the hydrostatic supporting surfaces 5. However, if the clearances between the land portions 8 and the outer surface of the second slide member 3 were increased, the supporting strength of the hydrostatically supporting device would be decreased.
Also, another type of hydrostatic supporting device is disclosed as a prior device in the Japanese unexamined patent application No. 59-13120. In this device, as shown in FIG. 3, a slider 12 is provided with sliding surfaces 14, whereat air pockets 15 extending along the sliding direction and plural T-shaped grooves 16 extending in lateral direction are formed. The grooves 16 are connected to the air pockets 15, and have a constant small depth to reduce the pressure of the air fed into the air pockets 15 gradually. Although this device has an advantage to reduce the number of nozzles, it is necessary to form a large number of T-shaped grooves 16 on the sliding surfaces 14, thereby the machining time of the device becoming long. Further, since no hydrostatic pressure pocket is formed at the lateral both ends of the sliding surface, it is difficult to increase the supporting strength against rolling motions.